The object of the present invention is an improvement in a gradient coil for image formation devices using nuclear magnetic resonance. The invention has special application in the medical field where image formation by nuclear magnetic resonance is unanimously acknowledged to be a diagnostic aid. Of course, it can be used in other fields. The goal of the present invention is to help create more faithful and higher-resolution images of a body to be examined.
A device for image formation by nuclear magnetic resonance comprises essentially three types of coils. An initial type of coil (which may be replaced if necessary by a permanent magnet) is aimed at creating a strong, homogeneous, magnetic field B.sub.0 in a pre-determined space. A second type of coil, known as a radiofrequency coil, is aimed at subjecting a body, which is examined and placed under the influence of the field of the first type of coil, to radiofrequency excitation sequences and at measuring the radiofrequency signal retransmitted by the particles of the body. The radiofrequency response is a response in volume: all the particles of a region of the body subjected to the examination transmit their radiofrequency responses at the same time. To create the image, it is necessary to differentiate among these responses. To this end, image formation devices comprise a third type of coils, known as gradient coils, to superimpose additional field components on the strong field. The value of these components is a function of the coordinates in space of their place of application. In other words, each position in space can be coded by a different field value: the resulting modifications are exploited in the retransmitted signal. Conventionally, it is proposed to structure this differentiation along three mutually perpendicular axes, X, Y, Z. By convention, the Z axis is co-linear with the strong field created by the coils of the first type.